Transmitters (e.g., magnetrons) and receivers (e.g., electronic components of reception circuits) provided in radar apparatuses may deteriorate as being used, or be damaged by a strong signal received externally. Thus, there has been a case where a radar performance monitor is provided to such a radar apparatus in order to check if the transmission intensity and the reception sensitivity of the radar apparatus are good.
This kind of radar apparatus generally includes a radar unit and a PM unit. The radar unit transceives radar signals and generates a radar image. The PM unit receives a radar signal transmitted from the radar unit and measures the transmission intensity. Moreover, the PM unit transmits a performance signal (hereinafter, referred to as the PM signal) after receiving the radar signal. The radar unit receives and analyzes the PM signal to measure the reception sensitivity of the radar apparatus. Each of JP2011-117808A and JP2011-117809A discloses such kind of radar apparatus provided with a performance monitor.
In the radar apparatus of JP2011-117808A, a transception circuit of the radar unit and a transception circuit of the PM unit are commonalized. Moreover, the radar apparatus can switch its mode between a mode in which the radar image is generated by transceiving the radar signals and a mode in which the transmission intensity and the reception sensitivity of the radar apparatus are measured as described above.
Here, in the case of measuring the performance of the radar apparatus by switching the mode as disclosed in JP2011-117808A, there is a disadvantage that the radar image cannot be updated while the performance of the radar apparatus is measured. The radar apparatus disclosed in JP2011-117809A solves this disadvantage.
In the radar apparatus of JP2011-117809A, similarly to the radar apparatus in JP2011-117808A, a transception circuit of the radar unit and a transception circuit of the PM unit are commonalized. Moreover, radar apparatuses generally detect, based on a time length from a transmission of a radar signal to a reception of the radar signal (an echo), a distance of the received echo. The radar apparatus of JP2011-117809A performs a transception of a PM signal and measures the performance of the radar apparatus after a period of time for the radar signal to travel a distance corresponding to the display distance range of the display unit from its transmission, but before the next radar signal is transmitted.
However, with the radar apparatus in JP2011-117809A, there has been a problem that a transmission cycle of the radar signal becomes slow. Especially when a radar signal with a long pulse width is transmitted for long distance detection, since a detection range in an azimuth direction becomes wider, a problem arises that the echo cannot be detected in a large area.
Moreover, in the radar apparatus of JP2011-117809A, even if the transmission cycle of the radar signal is shortened by sacrificing the reflection echo of the radar signal from a long distance area, a problem arises that a target at a distant location from the radar apparatus cannot be displayed.